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23  WEST  MAIN  STREET 

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The 
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0 


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16X 


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24X 


28X 


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pram:Are  page  qui  comporte  une  empreinto 
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la  darniire  page  qui  comporte  une  telle 
empreinte. 

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demi^re  image  de  cheque  microfiche,  aelon  le 
caa.  le  symbols  •-»>signifie  "A  SUIVRE",  la 
symbola  V  signifie  "FIN". 

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da  I'anqla  supAricur  gauche,  de  gauche  i  droite. 
et  dk  haut  en  baa.  en  prenant  le  nombre 
d'Imagea  nteessaire.  Lea  diagrammes  suivants 
illustrent  la  m^thoda. 


1 

2 

3 

4 

5 

6 

MC909 
•  V25a 


ii^.^ 


Reprinted  from  The  Journal  of  Geology,  Vol.  i,  No.  2, 
February-March,  1893. 


J.j-^^<^c 


=7  yy 


t 


\ 


AN 


Historical  Sketch 

OF    THE 

Lake  Superior  Region 

TO 

Cambrian  Time 


By    C.  R.  van  HISE 


I 


CHICAGO 
'  D.  C.  HEATH  &  CO.,  Directors 


■ 


■)• 


*!« 


' 


THE 


JOURNAL  OF  GEOLOGY 


FEBRUARY- MARCH,  iSgj. 


AN  HISTORICAL  SKETCH  OF  THE   LAKE  SUPERIOR 
RF:GI0N  to  CAMBRIAN  TIME.' 

(with    PLATE  I.) 


The  ancient  formations  south  of  Lake  Superior  may  be 
grouped  into  five  great  divisions  :  the  Basement  Complex,  the 
Lower  Huronian,  the  Upper  Huronian,  the  Keweenawan,  and 
the  Lake  Superior  Sandstone.  These  five  divisions  are  separated 
by  unconformities  of  great  magnitude,  two  of  them  at  least 
being  of  the  first  order.  According  to  the  classification  adopted 
by  the  United  States  Geological  Survey,  the  Basement  Complex 
is  Archcan  ;  the  Lower  Huronian,  Upper  Huronian  and  Kewee- 
nawan constitute  the  Algonkian  for  this  region  ;  and  the  Lake 
Superior  Sand.stone  is  Cambrian. 

The  Basenii  t  Complex. — The  characteristic  rocks  of  the 
Basement  Complex  are  (  i  )  light  colored  granites  and 
gneissoid  granites,  and  (2)  dark  colored  finely  foliated  or 
banded  gneisses  or  schists.  These  are  cut  by  various  basic  and 
acid  intrusives,  many  of  which  are  not  different  from  eruptives 

■In  this  very  general  article  no  attempt  will  he  made  to  give  references  to  the 
many  authors  from  whom  facts  are  taken.  To  give  full  credit  for  all  information 
used  would  require  citations  from  scores  of  papers.  The  writer  gives  a  summary 
of  the  literature  of  the  Lake  Superior  Region  in  Bulletin  86  of  the  U.  S.  Geo!. 
Survey. 

Many  of  the  problems  considered  have  no  definite  answers  as  yet.     The  aim  of 
the  article  is  to  give  a  summary  of  the  very  limited  knowledge  available  on  a  sub- 
ject that  has  not  before  been  considered,  because  the  data  were  not  at  hand  upon    , 
which  to  base  any  reliable  conclusions. 
Vol.   I. — No.  2. 


(;i:OLO(;i(  AL  MAPOKTHI-:  I.AKK  SI 

SJIOWINO  nil-.  CAMHUIAN   AXl)  CKYS'l 

Compiled  IrotnOllKinl  MopsolU  S.nncI  Oiiindit 

S<-rtle 
o  50  100 


PLATE    I 


AI.CiOXlUAK 

HAh     1  '    '   Ak      ! 


POST  AI.IUiNKlAX 

Ca      ! 


lii:  CAMHUIAN  AND  CKYSTAI.l.INH  HOCKS. 

)iied  irotnOll'KMrtI  Maps  of  l'  S.nnd  (lnii«Jiaii  Stirvcvs 

Scnio 

50  100  ISO    STAT   Ml. 


Ah  riici'riqiilill    ntllinrili  ,  ,.  , .  ,    ,, 

Ah2  riio  Miii-:iiwlli'     M"iuiiiiiiicr'  Iirn    //foi-iNi/  VVi'srs 

Ah  J  riirWi.'ilfjiisiii   Vdllrv  Slnt<:\ 

A  h  4  riic  Pi'iiolni-  !nni   Fi-iiniiii  S^/ll,s^^■ 

,    „ ,  ^,         i    Ah5  T/w  St.l,,,,.,.-.  .'H.ile.^ 

M  L'  R  ON  I  A  N  ^  ^  5  j-ii^  Chlripewf  fcilln-  QiKirtrlU'S 

A  h7  The  llldrlillivrrlmt   l!riiiiri<i  Srlus(s 

Ah8  -Iiic  Ihiri'lmnViiartxiirfi 

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A  h'O  ThfAilimiliu'SrrKs 

A  h  II  [''otdtfiSchist^nfCauitJn 


"^ 


114 


7///-;  J(H'N\AL  OF  GEOLOGY. 


fouiul  in  tbt;  later  scries,  with   which   they  arc  doubtless  in  part 

continuous. 

The  granites  and  gneissoid  granites  are  jilaccd  together,  be- 
cause between  the  two  are  constant  gradations.  If  one  speaks 
accurately  and  includes  among  granites  only  those  rocks  which 
are  completely  massive,  the  gneissoid  granites  include  the 
greater  part  of  ihe  granitic  rocks ;  for  in  large  exjmsures  it  is 
usually  possible  to  find  some  evidence  of  foliation.  The  granit- 
oid areas  are  of  greatly  varying  sizes,  runi\ing  from  small 
patches  to  those  many  miles  in  diameter.  When  everywhere 
surrounded  by  the  schistose  division  of  the  Basement  Con.plex, 
they  fre(p;ently  have  oval  or  ovoid  forms.  In  nearing  the  outer 
border  of  the  granitoid  areas,  the  foliation  often  becomes  more 
and  more  prominent,  and  near  the  edge  of  an  area  t..w  rock  fre- 
cjuently  passes  into  a  well  laminated  gneiss. 

The  schistose  rocks  include  fine  grained  hornblende -gneisses, 
mica -gneisses,  chlorite -gneisses,  and  various  green  schists,  for- 
merly sujjposed  to  be  sedimentary,  but  now  known  to  be  greatly 
modified  basic  and  acid  igneous  rocks.  These  schists  have 
usually  a  dark  green  or  black  color,  are  strongly  foliated,  and 
the  variations  in  strike  and  dij)  of  this  foliation,  within  small 
areas,  is  very  great.  Not  infrecjuently  the  schistose  rocks  are 
traced  by  gradations  into  massive  igneous  rocks. 

The  contacts  between  the  schistose  division  and   the  granit- 
oid division  of  the  Basement  Comjilex  are   usually  those  of  in- 
trusion, the  granitoid  rocks  being  the  later.      In  i)assing  from  a 
schistose  to  a   granitoid  area,  small   pegmatitic   looking  veins  of 
the  granite  are  first  found.      In  going  onward  these  veins  beconie 
more  numerous  and.  after  a  time,  unmistakable  dikes  of  granite 
ai)pear.  which  multiply   in   number  and   size   in  aj)proaching  the 
granite  area,  until  the  granite  is  found  in  great  bosses.      Here  we 
have  i)erhaps  a  nearly   ecjual   c|uantity  of  schistos.:  and  granitoid 
rocks,  and  in  this  intermediate  zone  the   schists  may  be  found  as 
a  mass  of  blocks  within  the  granite,  soinetimes  at  but  -mall  dis- 
tances from  their  original  positions,  the   whoie  having  rretiucntly 
a  somewhat  ct)ng!omeratic  api)earance.      However,  these  jiseudo- 


"^ 


///ST(>A'fCAL  Sr-ETClf    I.AKK  SUPKRfOR  REGION. 


"5 


conglomerates,  so  well  describcl  by  La. /son,  grade  more  or  less 
rapidly  on  the  one  hand  into  the  schists,  and  on  the  other  into 
the  solid  gneissoid  granite.  The  complete  cjiaiigf  may  occur 
within  a  short  distance,  or  it  may  take  a  mile  oi  more. 

The  Hasement  Complex  is  then  composed  of  intricately  inter- 
locking areas  of  granitoitl  rocks  and  schistose  rocks.  Moreover, 
all  of  these  rocks  are  completely  crystalline.  None  of  them 
show  any  vmiuistakable  evidence  of  havinii^  been  derived  from 
sedimentaries,  but  many  can  be  traced  with  gradations  into 
massive  rocks,  and  there,  jre  the  greater  jjroportion  of  them  are 
igneous,  if  a  comjiletely  massive  granular  structure  be  proof  of 
such  an  origin. 

"^he  Hasement  Complex  is  the  most  widespread  of  any  of  the 
Lak«.  Superior  systems,  and  it  tic  'nless  runs  under  all  later  for- 
matioi  s  to  a  greater  or  lesser  distance.  That  it  is  continuous  un- 
der all  such  formations  can  not  be  asserted,  for  while  it  was  once 
so,  it  is  j)ossible.  perhaps  even  probable,  that  in  places,  as  a  con- 
se(juence  of  sedimentation  and  folding,  the  Basement  Complex 
has  oeen  so  deeply  buried,  that  fusion  has  locally  resulted.  It 
is  even  possible  that  such  fused  material  is  a  partial  source  of  the 
later  volcanic  eruptions. 

Before  the  earliest  sedimentary  rocks  were  dejjosited,  the 
Basement  Complex  was  subjected  to  enormous  orographic  forces, 
which  folded  and  sheared  the  rocks  in  a  most  intricate  manner. 
Accompanying  the  great  orographic  movements,  which  undoubt- 
edly occupied  a  vast  period  of  time,  were  intrusions  of  various 
deep  seated  igneous  rocks,  and  also  doubtless  their  volcanic 
e<]uivalents  were  extruded.  Subsei]uent  to,  and  during  the  oro- 
graphic mo  ements,  atmospheric  forces  were  at  work.  Erosion 
continued  long  after  the  mountain -making  folding  had  ceased, 
and,  for  much  of  the  Lake  Superior  region,  reduced  the  Base- 
ment Complex  nearly  to  a  plain  or  base  level.  As  evidence  of 
this  may  be  cited  the  fact  that,  at  the  end  of  the  erosion  inter- 
val, the  Basement  Complex,  consisting  of  differing  lithological 
materials,  and  therefore  having  a  variable  resisting  power,  did 
not  vary  in  alti'     'e  more  than  a  few    hundred    feet    for  long  dis- 


I 


,l6  THE  JOURNAL  OF  GEOLOGY.      ' 

tances.  Whether  this  denudation  extended  everywhere  deep 
enough  to  remove  all  surface  vole  ■  .lic  material,  and  to  leave  only 
deep  seated  igneous  material,  is  undetermined.  At  the  beginnmg 
of  the  Lower  Huronian  time,  the  Basement  Complex  was,  in  the 
Lake  Superior  region,  a  universal  system. 

The  Lower  Huronian.— Mi^x  the  forces  of  erosion  had  nearly 
exhausted  themselves,  there  was  the  f^rst  advance  of  the  sea  over 
the  Lake  Superior  region  of  which  we  have  any  evidence,  as  a 
result  of  which  the  Lower  Huronian  was  deposited. 

The  well-known  characteristic  rocks  of  the  Lower  Huronian. 
are  (i)  conglomerates,  quartzites,  quartz -schists  and  mica- 
'.rhists.  (2)  limestones.  (3)  various  ferruginous  schists.  (4)  baste 
uid  acid  eruptives.  which  occur  both  as  deep  seated  and  as  effu- 
sive rocks.  The  order  given,  with  the  exception  of  the  erup- 
tives. is  the  order  of  age  from  the  base  upward. 

The  inferior  formation  is  usually  a  quartzite  or  a  feldspathic 
quartzite      Where  metamorpbism  has  been  severe  it  passes  into  a 
quartz -schist,    mica -schist    or    gneiss.     The    lowest  horizon  of 
the  formation  is  in  places  a  coarse  conglomerate,  and  this  when 
metamorphosed  may  become  a  conglomerate -schist.     This  con- 
glomerate is  of  two  types,  depending  upon  the  character  of  the 
underlying  formation,  which  is  here  granitic  and  there  schistic. 
The  limestone  formation,  when  at  its  maximum,  is  of  very  con- 
siderable thickness.     The    limestone    is  magnesian  and  so  very 
crystalline    as    to    make  the  name  marble  appropriate.     It  fre- 
quently contains  a  considerable  amount  of  chert.     In  places  it 
maybe  divided  into  two  horizons, , one  of  which  is  nearly  pure 
marble,  and  the  other  nearly  pure    chert.     At  other  times  the 
limestone   becomes   very  siliceous  by  a  mingling  of  fragmental 
quartz,  while  zones  of  wholly  fragmental  material    may  occur. 
These  impure  phases  are  often  at  the  lower  part  of  the  limestones. 
where  they  may  be  considered  as  a  transition  from  the  under- 
lying   formation.      The    formation    overlying    the    limestone    is 
usually  known  as  the  iron -bearing  member,  since  it  contains  all 
the  ore  bodies  of  the  Lower  Huronian.   It  has  varied  aspects,  but 
the  different  varieties  grade  into  one  another  )*oth  vertically  and 


I 


HISTORICAL  SKETCH— LAKE  SUPERIOR  REGION.       I  I  ^ 


k 


laterally,  so  that  when  one  becomes  familiar  with  them,  the  rocks 
of  the  formation  may  invariably  be  recognized.  Here  are  included 
hematitic  and  magnctitic  schists,  cherts,  jaspers,  ferruginous 
carbonates,  and  other  forms.  The  formation  always  differs  from 
the  limestone  in  carrying  a  very  considerable  amount  of  iron,  and 
it  differs  from  the  quartzite  in  being  largely,  and  sometimes 
wholly,  a  chemical  or  organic  sediment,  rather  than  a  mechani- 
cal one. 

The  three  members  of  the  Lower  Huronian  are  not  often  seen 
in  a  single  section.  This  may  be  due  to  lack  of  exposures,  but 
in  some  case^  is  undoubtedly  due  to  the  absence  of  one  or  more 
of  the  formations  themselves. 

In  the  Lower  Huronian,  basic  eruptive  rocks  are  abundant, 
and  locally  cover  considerable  areas.  Not  infrequently  acid 
eruptives  also  occur.  These  eruptives  include  both  contempor- 
aneous volcanics  and  subsequent  intrusives.  If- the  Keewatin  of 
Lawson  about  Rainy  Lake  and  the  Lake  of  the  Woods  is  Lower 
Hurnian,  great  granitic  masses  have  been  intruded  into  this 
series  northwest  of  Lake  Superior. 

Equivalent  to  the  Lower  Huronian  series  of  the  north  shore 
of  Lake  Huron  are  placed  the  following  iron-bearing  districts : 
Lower  Vermillion,  Lower  Marquette,  Felch  Mountain,  in  large 
part.  Lower  Menominee,  the  cherty  limestone  formation  of  the 
Penokee  district ;  and  probably  the  Kaministiquia  series  of 
Ontario,  and  the  Black  River  Falls  series  of  Wisconsin.  Whether 
all  of  these  detached  basins  were  once  connected  by  continuous 
sediments  is  unknown,  but  probably  they  were. 

The  fragmental  material  of  the  Lower  Huronian  was  derived 
from  the  Basement  Complex.  This  fragmental  formation  is  usu- 
ally thin.  This  doubtless  means  that  the  advance  of  the  sea 
over  the  Lake  .Superior  region  was  comparatively  rapid.  The 
directions  from  which  the  Lower  Huronion  sea  entered,  and  the 
extent  of  its  trangrcssion.  is  at  present  unknown.  By  certain  of 
the  Canadian  geologists  it  is  held  that  the  structural  break  which 
exists  between  the  Basement  Complex  and  the  Lower  Huronian, 
south  of  Lake  Superior  and  north  of  Lake  Huron,  does  not  exist 


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THE  JOURNAL  QP  GEOLOGY. 


in  the  region  of  Rainv  Lake  and  Lake  of  the  Woods,  northwest 
of  Lake  Superior.  If  this  conclusion  be  true,  the  sea  did  not 
advance  as  far  as  the  Lake  of  the  Woods,  this  district  perhaps 
being  above  the  ocean,  and  one  of  the  sources  of  detritus  through- 
out Lower  Huronian  time. 

The  extent  of  1he  Lower  Huronian  deposits  is  also  uncertain. 
If  the  series  of  the  districts  above  placed  in  the  Lower  Huronian. 
are  correctly  correlated.  Lower  Huronian  basins  occurred  in  vari- 
ous places  over  a  great  triangular  area  extending  from  Black 
River  Falls  in  Wisconsin,  to  northeastern  Minnesota,  and  thence 
east  to  the  north  shore  of  Lake  Huron.  Doubtless  Lower 
Huronian  rocks  also  occur  in  the  great  northern  region  of 
Canada,  and  they  may  have  had  a  much  wider  original  extent 
than  this,  but  no  data  are  now  available  to  locate  such  a  possible 
extension. 

Of  the  original  thickness  of  the  Lower  Huronian  dejwsits  we 
are  also  ignorant.  The  present  thickness  has  not  been  deter- 
mined south  of  Lake  Sui)erior,  but  according  to  Logan,  on  the 
north  shore  of  Lake  Huron,  including  the  interstratified  volcanics, 
the  thickiiess  is  five  thousand  feet. 

At  the  end  of  Lower  Huronian  time,  the  Lake  Superior 
region  was  raised  above  the  sea,  folded,  and  subjected  to  erosion. 
The  orographic  movements  of  this  time  were  very  severe,  closely 
crumpling  in  places  the  rocks  of  the  Lower  Huronian,  and  induc- 
ing in  them  in  many  places  a  schistose  structure.  In  other  locali- 
ties, away  from  the  axes  of  great  disturbance,  the  Lower 
Huronian  rocks  were  but  gently  tilted,  as  is  shown  by  the  small 
discordance  in  places  between  them  and  the  succeeding  scries. 
In  certain  localities  the  areas  of  great  disturbance  are  but  a  short 
distance  from  those  of  comi)arative  (juiet.  The  denudation  was 
deep  enough  to  wholly  remove  the  entire  series  over  wide  areas, 
and  to  cut  to  unknown  depths  into  the  Basement  Comi)lex  itself. 
As  has  been  stated,  the  Lower  Huronian  has  an  estimated  thick- 
ness of  about  one  mile  on  the  north  shore  of  Lake  Huron,  and 
in  different  localities  varies  from  this  thickness  to  entire  absence, 
depending  mainly  upon  the  differing  deundation.     This  variabil- 


HISTORICAL  SKETCH^LAKE  SUPERIOR  REGION.       II9 


J 


ity  may  possibly  be  due  in  part  to  highlands  of  the  Basement 
Complex,  which  were  not  covered  by  the  Lower  Huronian  sea 
until  the  period  was  well  advanced.  Of  the  extent  of  the  series 
at  the  end  of  the  erosion  preceding  Upper  Huronian  deposition, 
little  has  been  determined,  since  later  erosions  have  undoubtedly 
removed  large  areas  of  the  series,  and  therefore  its  present  dis- 
tribution is  not  a  safe  guide  to  its  distribution  at  the  close  of  the 
erosion  interval  referred  to. 

The  Upper  Huronian. — At  the  close  of  the  long  period  of 
erosion  which  followed  the  Lower  Huronian  deposition,  the 
water  once  more  advanced  upon  the  Lake  Superior  region,  and 
the  Upper  Huronian  series  was  deposited. 

Lithologically  this  series  consists  of  conglomerates,  quartzites, 
graywackes,  graywacke-slates,  shales,  mica-schists,  ferruginous 
slates,  cherts,  jaspers,  ferruginous  schists  and  igneous  rocks, 
including  both  lava  flows  and  volcanic  fragmentals,  as  well  as 
basic  and  acid  intrusives.  The  series,  as  a  whole,  is  very  much 
less  crystalline  than  the  Lower  Huronian,  although  locally  the 
shales  and  graywackes  l.ave  been  transformed  into  mica-schists, 
and  even  into  gneisses. 

.''*  The  Upper  Huronian  immediately  about  Lake  Superior  is 
divisible  into  three  formations,  a  lower  slate,  an  iron-bearing  for- 
mation, and  an  upper  slate,  the  basis  of  separation  being  that  of 
mechanical  and  non-mechanical  detritus.  The  inferior  formation 
is  mainly  a  cjuartzose  slate  or  shale,  but  locally  it  [)asses  into  a 
quartzite,  while  the  basal  horizon  is  frequently  a  conglomerate. 
The  nature  of  this  conglomerate  varies  greatly,  depending  upon 
the  character  of  the  underlying  formation,  which,  in  some  areas, 
is  the  Basement  Complex,  and  in  others  the  Lower  Huronian. 
In  the  first  case  the  slates  may  rest  upon  the  gneissoid  granite, 
upon  the  schis  :,  or  upon  the  junction  of  the  two.  The  basal 
conglomerate  corresponds  in  its  character,  being  a  recomposed 
granite  or  granite-coaglomcrate,  a  recomposed  schist  or  schist 
conglomerate,  or  finally  a  combination  of  the  two. 

When  the  lowest  member  of  the  Uj)pcr  Huronian  rests  upon 
the   Lower   Huronian   series,  the  underlying  lOrniation  may  be 


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THE  JOURNAL  OF  GEOLOGY. 


any  one  of  the  three  formations  of  the  Lower  Huronian.  As  a 
conse(}uence  the  basal  conglomerate  may  consist  mainly  of  the 
fragments  of  any  one  of  these  formations,  or  of  all  of  them 
together.  Not  infrequently  detritus,  derived  from  the  Basement 
Complex,  is  mingled  with  that  of  Lower  Huronian  origin.  How- 
ever, as  a  consequence  of  the  resistant  character  of  the  jaspery 
iron-bearing  formation  of  the  Lower  Huronian  and  of  mining 
operations,  the  discovered  contacts  are  most  frequently  between 
the  Upper  Huronian  and  this  iron-bearing  formation.  In  the 
basal  conglomerate  or  recomposed  rock  at  these  points,  the 
characteristic  fragments  are  chert,  jasper,  and  other  ferruginous 
materials,  and  it  is  locally  so  rich  in  iron  as  to  bear  ore-bodies. 
The  uppermost  horizon  of  the  lower  slate  of  the  Upper  Huronian 
in  the  Penokee  district  is  a  pure,  persistent  layer  of  quartzite. 
The  central  mass  of  the  formation  is  a  graywacke  or  graywacke- 
slate,  passing  in  places  into  a  shale  or  sandstone. 

Above  the  lower  slate  is  the  iron-bearing  member,  consisting 
of  variou'=  ferruginous  rocks,  including  cherts,  jaspers,  magnetite- 
actinolite-schists,  iron  ores,  and  ferruginous  carbonates.  It  has 
been  shown  that  all  these  varieties  have  been  mainly  derived 
directly  or  indirectly  by  transformation  from  an  original  lean, 
iron-bearing  carbonate,  which  was  of  chemical  or  organic  origin, 
or  a  combination  of  both.  Mingled  with  these  non-mechanical 
sediments  is  a  greater  or  lesser  quantity  of  mechanical  detritus. 

Above  the  iron-bearing  formation  is  the  upper  slate  forma- 
tion. This  is  mainly  composed  of  shales  frequently  carbon- 
aceous or  graphitic,  slates,  graywackes  and  mica-schists,  often 
garnetiferous  and  staurolitic.  The  mica-schists  are  usually 
toward  the  upper  part  of  the  formation.  The  stages  of  the 
transformation  between  these  crystalline  rocks  and  plainly 
fragmental  detritus  have  been  somewhat  fully  made  out . 

The  lower  slate  formation  is  of  variable  thickness,  but  is 
usually  less  than  a  thousand  feet.  The  iron-bearing  formation  is 
also  of  very  variable  thickness,  its  maximum  being  perhaps  about 
the  same  as  that  of  the  lower  slate,  and  from  this  it  varies  to  dis- 
appearance, the  horizon  being  usually  represented,  however,  by 


I 
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HISTORICAL  SKETCH— LAKE  SUPERIOR  REGION.       121 


I 
I 


carbonaceous  and  ferruginous  shales  and  slates.  The  upper 
slate  formation  includes  the  great  mass  of  the  Upper  Huronian 
series.     Its  maximum  thickness  is  more  than  ten  thousand  feet. 

In  certain  areas,  during  Upper  Huronian  time,  there  was 
great  volcanic  activity,  as  a  result  of  which,  peculiar  formations 
were  piled  up,  wholly  different  from  any  of  the  ordinary  mem- 
bers of  the  series.  Also  this  volcanic  activity  greatly  disturbed 
the  regular  succession,  so  that  for  each  of  the  volcanic  districts 
an  independent  succession  exists,  the  sedimentary  and  volcanic 
formations  being  intir>iately  interlaminated.  The  two  areas 
which  are  best  known  are  the  Michigamme  iron  district  north 
of  Crystal  Falls  and  the  east  end  of  the  Penokee  district. 
Similar  volcanics  also  occur  in  the  Marquette  district.  In 
the  Michigamme  iron  district  is  an  extensive  area  of  green- 
stones, greenstone -conglomerates,  agglomerates  and  surface 
lava  flows,  many  of  which  are  amygdaloidal.  In  the  Penokee 
district  the  materials  are  almost  identical.  The  typical  suc- 
cession for  this  district  extends  in  unbroken  order  for  fifty 
miles  or  more,  but  east  of  Sunday  L?,ke  this  is  suddenly  dis- 
turbed by  the  appearance  of  the  volcanics.  The  character  of  the 
rocks  and  their  order  soon  becomes  so  different  that  if  one  were 
not  able  to  trace  the  change  from  one  into  the  other,  there  would 
be  a  great  temptation  to  regard  the  part  of  the  series  bearing 
volcanics  earlier  than  or  later  than  the  Penokee  series  proper. 
But  the  continuity  of  the  two  cannot  be  doubted.  Thus  this 
occurrence  well  illustrates  that  lithological  character  in  pre- 
Cambrian,  as  in  post-Cambrian  time  is  no  certain  guide  as  to 
relative  age.  Finally,  associated  with  the  Lake  Superior  Upper 
Huronian  rocks  are  many  later  intrusive  dikes  and  interbedded 
sills,  chiefly  diabases,  gabbros  and  diorites,  but  local  granitic 
intrusives  also  occur,  particularly  in  the  Felch  Mountain  and 
Crystal  Falls  districts,  and  possibly  also  in  the  Menominee 
district. 

The  typical  districts  in  which  the  Upper  Huronian  series  can 
be  best  studied  are  the  Penokee,  Marquette,  Mesabi  and  Animikie. 
Remote  from  the  Lake  Superior  region  proper,  the  rock  series 


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which  arc  correlated  with  the  Upper  Huronian  have  not  the  same 
successions  of  formations  as  in  these  districts.  The  Upper 
Huronian  north  of  Lake  Huron  has  a  set  of  formations  which 
can  not  be  correllated  with  the  formations  above  given  ;  the  same 
is  uue  of  other  series  to  the  south  which  arc  here  placed.  The 
position  of  these  latter  as  a  part  of  the  Upper  Huronian  must 
not  be  considered  as  a  question  finally  determined,  but  rather  as 
representing  the  probability,  from  the  weight  of  evidence  at  the 
present  time.  It  can  not  be  expected  that  in  a  great  geological 
basin  the  same  subordinate  succession  of  formations  will  be 
everywhere  found. 

However,  for  the  present,  regarding  all  these  series  as  Upper 
Huronian,  this  is  the  most  widespread  of  the  Lake  Superior  pre- 
Cambrian  sedimentary  series.  It  includes  a  great  area,  extending 
from  the  Sioux  quartzites  of  Dakota  on  the  southwest,  to  the 
Huronian  rocks  north  of  Lake  Huron  on  the  east,  and  thence  far 
to  the  north,  and  from  Lake  Huron  to  the  Animikie  series  of  the 
National  Boundary  west  of  Lake  Superior.  Within  this  area 
are  included  the  major  portion  of  the  Baraboo  quartzites  of 
Wisconsin;  the  major  portion  of  the  large  area  in  the  Upper 
Peninsula  of  Michigan,  the  eastern  arms  of  which  are  the  Menom- 
inee, Felch  Mountain,  and  Marquette  iron-bearing  districts  ;  the 
greater  part  of  the  Penokee-Gogebic  iron-bearing  series  of 
Michigan  and  Wisconsin  ;  the  Chippewa  quartzites  of  Wisconsin  ; 
St.  Louis  slates  of  Minnesota  including  the  newly  developed 
Mesabi  range  of  Minnesota,  and  the  i^nimikie  scries  of  Thunder 
Bay,  Lake  Superior  and  its  westward  extension.  That  most,  and 
perhaps  all  of  these  areas  were  once  connected,  there  can  be  no 
reasonable  doubt. 

This  broad  semicircular  zone  of  Upper  Huronian  rocks,  extend- 
ing from  the  National  Boundary  west  of  Lake  Superior  through 
Ontario,  Minnesota,  Michigan  and  Wisconsin,  to  the  north 
Channel  of  Lake  Huron,  and  thence  north  to  the  east  side  of  James 
Bay,  suggests  that  the  transgression  of  the  sea  was  from  the 
south  and  east,  and  that  the  source  of  the  mechanical  detritus  is 
the  great  expanse  of  so-called  Laurentian  rocks  west  of  Hudson 


i. 


HISTORICAL  SKETCH—LAKE  SUPERIOR  REGION.       1 23 


I 


Bay  and  north  of  Lake  Superior.  How  far  the  sea  transgressed 
over  this  aieri,  and  whether  it  also  advanced  toward  it  from  the 
north  and  west,  is  unknown.  It  is  probable  as  the  sea  advanced 
from  the  south,  that  the  great  mass  of  fragmental  detritus,  mak- 
ing up  the  Baraboo  and  Sioux  quartzites,  was  laid  down  before 
the  sea  had  transgressed  to  what  is  now  the  north  shore  of  Lake 
Superior,  and  thus  would  be  explained  the  discrepancy  in  the 
parallelism  of  formation  between  the  Sioux  quartzites,  Baraboo 
(juartzites,  etc.,  and  the  districts  of  Upper  Huronian  rocks  adja- 
cent to   Lake  Superior. 

In  this  case  the  advancing  ocean  was  perhaps  making  its 
progress  by  cutting  a  terrace  (juite  as  much  as  by  subsidence. 
However,  there  is  reason  to  believe  that  the  area  included  within 
the  west  end  of  the  Lake  Superior  Basin,  /.  e.,  from  the  Animikie 
series  to  the  Mesabi  range,  and  thence  to  the  Penokee  series  was 
submerged  practically  at  the  same  time.  For  here  we  have  three 
great  formations  of  like  character  in  identical  order.  The  lowest 
formation,  the  quartzite  and  quartz-sl?te  with  conglomerates 
derived  from  the  Basement  Complex  a  id  the  Lower  Huronian, 
are  the  first  deposit  of  the  advancing  sea.  After  this  came  a 
deepening  of  the  water,  when  the  calcareous  and  ferruginous 
formation,  now  constituting  the  iron-bearing  member,  was  laid 
down.  Then  perhaps  as  a  consequence  of  the  upbuilding  of  this 
formation,  came  a  shallowing  of  the  water  and  the  deposition  of 
the  great  thickness  of  clayey  sediments  of  the  Upper  Huronian. 
Since  the  last  formation  must  have  been  deposited  in  shallow 
water,  and  yet  is  of  great  thickness,  the  bed  of  the  ocean  was 
probably  subsiding  during  the  remainder  of  Upper  Huronian 
time. 

At  the  end  of  the  deposition  of  the  Upper  Huronian  rocks, 
the  Lake  Superior  region  rose  above  the  sea,  and  the  atmospheric 
forces  once  more  set  to  work.  The  orographic  movement  follow- 
ing the  Upper  Huronian,  like  that  following  the  Lower  Huronian, 
was  locally  intense,  but  in  general  the  folding  was  of  a  gentle 
character.  Along  narrow  axes  the  plications  were  so  severe  as 
to  give  the  Upper  Huronian  rocks  a  foliated  structure  and  com- 


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THE  JOURNAL  OF  GEOLOGY. 


pletely  crystalline  schistose  or  gneissic  character,  but  for  the 
most  part  the  changes  in  the  Upper  Huronian  rocks  are  those  of 
cementation  and  metasomatism.  As  with  the  Lower  Huronian 
areas  of  intense  plication,  they  are  sometimes  but  short  distances 
from   those  in  which  the  rocks  have  been  .merely  tilted.  ■ 

How  deep  the  Ujjper  Huronian  denudation  went  it  is  impos- 
sible to  say.  We  only  know  that  at  a  maximum,  the  Ujiper 
Huronian  rocks  are  now  13,000  feet  thick,  and  in  certain  other 
places  are  entirely  absent,  the  higher  members  disappearing  first 
and  the  lower  members  last.  Thus  the  difference  of  the  Upper 
Huronian  denudation  is  measured  by  13,000  feet.  To  this  must 
be  added  the  unknown  thickness  of  the  Upper  Huronian  rocks, 
which  have  been  wholly  swept  away,  and  the  thickness  of  the 
Lower  Huronian  and  Basement  Complex,  which  were  cut  at  this 
time.  The  thickness  represented  by  these  three  elements  is 
unknown,  but  it  is  probably  great. 

Of  the  outer  limits  of  the  Upper  Huronian  transgression,  we 
are  as  ignorant  as  of  the  jireceding  ones,  but  certain  it  is  that  it 
had  an  extent  to  the  outer  areas  mentioned  as  belonging  to  this 
series.  Beyond  these  limits  no  knowledge  is  available.  The 
original  extent  to  the  east,  south  and  west  of  the  Upper  Huronian 
will  pi-obably  ne'C^er  be. determined,  s-ince  the  ancient  rocks  are 
covered  by  the  Cambrian  and  post-Cambrian  sediments  Whether 
the  transgression  extended  over  the  Great  Northern  area  of 
Canada  to  the  Paleozoic  deposits  will  doubtless  be  ascertained 
when  th's  vast  region  is  studied  in  detail. 

The  Keiveenmvan. — Again  a  change  of  conditions  occurred, 
and  a  great  flood  of  basic  volcanics.  in  beds  of  enormous  thick- 
ness were  poured  out.  Later  these  were  followed  by  more  thinly 
bedded  volcanics.  At  about  the  same  time  a  portion,  at  least,  of 
the  Lake  Superior  region  became  immersed  in  the  sea,  since  in 
places  the  basement  lavas  of  the  Keweenawan  are  interstratificd 
with  sandstone  and  conglomerates. 

The  Keweenaw  series  is  composed  lithologically  of  gabbros, 
diabases,  porphyrites,  amygdaloids,  felsites,  quartz-porphyries, 
etc.,  and  of  sandstones  and  conglomerates.     The  basic  and  acid 


HISTORICAL  SKETCH-LAKE  SUPERIOR  REGIOW       12$ 

rocks  constituting  the  scries  are  mainly  surface  flows.  The  gab- 
bro  flows  are  often  of  immense  thickness.  The  diabase  flows 
are  usually  much  thinner,  and  frecjuently  pass  in  their  upper  parts 
into  porphyrites  and  amygdaloids.  Many  flows  are  porphyritic 
or  amygdaloidal  throughout.  The  beds  of  quartz-porphyry  and 
felsite  are  abundant  in  certain  districts,  bvit  usually  have  no  great 
lateral  extent,  but  while  a  single  flow  may  be  traced  but  a  little 
way,  frequently  a  grouj)  of  flows  of  the  same  general  character 
may  have  a  great  extent  and  thickness.  But  even  the  groups  of 
flows  cannot  be  regarded  as  general  formations  for  the  whole  of 
the  Lake  Superior  basin. 

Since  the  number  and  thickness  df  the  volcanic  beds  as  well 
as  the  detritals  vary  greatly,  the  Keweenaw   series  as  a   whole 
is  widely  variable  in  different  districts  in  its  character  and  thick- 
ness.    Structurally,  Irving  has  divided  the  series  into  two  parts, 
a  lower  division,  in  which  eruptives  are  present,  and  an  upper 
division,  in  which  eruptives  are  absent.     In  any  one  section  of 
the  Keweenawan,  at  the  lower  part  of  the  lower  division,  are 
generally  found  numerous  volcanic  flows,  with  few  or  no  detrital 
beds.     In  passing  toward  the  middle  of  the  series  the  sandstones 
and   conglomerates   become   more   and   more   numerous  and  of 
greater  thickness.     Still  higher  the  sandstones  and  conglomerates 
become  predominant,  and  finally   volcanic   products  disappear, 
the  upper  ten  or  fifteen  thousand  fe'et  of  the  Keweenaw  series 
being  wholly  composed  of  mechanical  detritus.     A  given  detrital 
bed  varies  from  a  mere  seam  of  narrow  local  extent  to  thick  beds 
of  sandstone  and  conglomerate,  one  of  which  has  been  traced, 
by  Marvine  for  more  than  one  hundred  miles.     The  most  gen- 
eral detrital  formation  is  the  upper  sandstone  and  conglomerate. 
The  Keweenawan  rocks  extend  about  the  entire  area  of  the 
Lake  Superior  basin.     They  appear  upon  the  east  shore  of  Lake 
Superior,  cover  a  large  area  of  Keweenaw  Point,  northern  Wis- 
consin, eastern    and    northeastern  Minnesota,  and  a  great  area 
about  Lake   Nipigon.     A  similar  set  of  volcanics,  occupying  a 
like  stratigraphical  position,  is  also  known  adjacent  to  Hudson 
Bay,  and  this  may  be  a  contemporaneous  series. 


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The  KcwcenawcMi  is  the  thickest  of  the  series  about  Lake 
Superior,  its  maximum  beinjr  estimated  by  Irvin^r  at  the  Montreal 
river  to  be  fifty  thousand  feet.  From  this  thickness  it  varies  to 
nothing.  This  vast  cjuantity  of  material  does  not,  however,  of 
necessity  mark  a  jjeriod  longer  or  perhaps  even  as  long  as  the 
Lower  Huronian  or  Upper  Huronian,  for  the  greater  part  of  it 
is  of  igneous  origin.  The  lava  fiows  in  their  e.xtent  and  thick- 
ness are  to  be  conijjared  with  the  great  volcanic  plateaux  of  the 
far  West,  rathe*-  than  with  local  volcanoes  such  as  Vesuvius,  or 
the  local  volcanoes  of  the  Upper  Huronian  and  Lower  Huronian. 
Associated  with  the  lavas  no  volcanic  fragmcntal  material  has 
been  as  yet  discovered. 

The  source  of  the  lavat:  of  the  Kewecnawan  is  beyond  the 
scope  of  this  paper.  It  was,  however,  suggested  that  the  fusion 
of  a  portion  of  the  Basement  Complex,  and  even  Lower  Huron- 
ian. may  have  in  part  jjroduced  the  deejj-seated  magmas,  the 
extrusion  of  which  produced  the  Kewecnawan  lavas. 

In  large  measure  the  sandstones  and  conglomerates  derived 
their  materials  from  the  volcanics  of  the  series,  but  a  lesser  (|uan- 
tity  came  from  earlier  series.  This  latter  is  jjarticularly  true  of 
the  great  detrital  formation  constituting  the  topmost  member  of 
the  Kewecnawan.  Partly  because  fragments  derived  from  the  fel- 
sites  and  porphyries  are  more  resistant  than  those  frcin  the  basic 
rocks,  acid  pebbles  are  relatively  abundant  in  the  conglomerates. 

The  fact  that  erosion  was  contemi^oraneous  with  erui)tion  for 
much  of  Kewecnawan  time  is  to  be  noted.  Certainly,  when  the 
period  was  well  inaugurated,  most  of  the  Lake  Superior  basin 
was  normally  below  the  sea  or  near  tide  water.  Many  of  the 
eruptions  may  have  been  sub-atiucous.  Here  and  there  volcanic 
masses  of  such  magnitude  were  built  u|)  as  to  rise  above  the 
water,  and  ujjon  such  areas,  the  sea  at  the  base,  and  vhe  air  and 
rain  above,  immediately  began  their  course  of  destruction.  The 
acid  and  more  viscous  lavas  may  have  formed  the  more  i)romi- 
nent  elevations,  and  thus  the  attack  was  here  more  vigorous. 
This  may  partly  explain  the  predominance  of  the  acid  pebbles 
in  the  conglomerates. 


HISTORICAL  SKETCH -LAKE  SUPERIOR  REGION.       I  27 


This  j^rcat  volcanic  period  was  doublcss  one  of  unstable 
equilibrium,  the  lithosphere  fallinj^  here  anil  rising  there.  One 
of  the  final  movements  was  the  production  of  the  Lake  Superior 
synclinal.  This  synclinal  movement  affects  not  only  the 
Keweenawan  rocks,  but  the  lower  series,  and  in  areas  in  which 
the  unconformity  between  the  Upjier  Huronian  and  the  Kewee- 
nawan is  not  grjat,  there  is  such  a  likeness  in  strike  and  dip  of 
the  two  series  as  to  suji^gest,  at  first,  that  the  two  are  conform- 
able. It  is  only  as  the  contacts  between  them  are  followed  for 
some  distance,  and  the  Keweenawan  is  seen  to  be  now  in  contact 
with  one  member  of  the  Upper  Huronian,  and  now  with  another, 
that  it  is  perceived  that  between  the  two  there  is  an  uncon- 
formity. 

What  proportion  of  the  Keweenawan  had  accumulated  before 
this  Lake  Superior  synclinal  began  it  is  impossible  to  say.  Pos- 
sibly somewhere  near  the  center  of  the  Lake  Superior  I  asin  were 
the  larger  foci,  from  which  the  great  extrusions  of  lava  occurred, 
and  here  a  simultaneous  sinking  went  on,  such  as  is  usual  as  a 
result  of  the  upbuilding  of  a  mountainous  mass  of  volcanic 
material.  This  suggestion,  if  true,  would  also  jiartly  explain  the 
apparent  absence  of  volcanic  fragmental  material  which  naturally 
would  accumulate  near  these  foci. 

Nowhere  are  the  Keweenawan  rocks  so  closely  folded  as  to 
give  them  a  schistose  structure  or  a  metamorphic  character. 
Their  induration  is  almost  wholly  a  process  of  cementation. 

The  Cambrian  Transgression. — At  the  close  of  Keweenawan 
deposition  the  Lake  Superior  region  was  again  raised  above  the 
sea,  and  the  pre-Cambrian  erosion  continued  until  the  enormous 
thickness  of  Keweenawan  deposits  was  wholly  truncated.  What 
must  have  been  mighty  mountains  were  reduced  to  mere  stumps, 
or  to  base  level.  Following  this  denudation,  the  sea  once 
more  transgressed  upon  the  land,  and  the  horizontal  Lake  Su- 
perior sandstone  was  deposited.  It  now  occupies  many  of  the 
bays  about  Lake  Superior.  It  once  was  much  thicker,  and  per- 
haps covered  all  but  the  highest  points  of  land.  Certainly  it  or 
an  overlying  formation  once  was  at  least  one  thousand  feet  higher 


I 


128 


THE  JOURNAL  OF  GEOLOGY. 


than  the  level  of  Lake  Superior,  but  it  has  since  been  almost 
completely  removed,  so  that  it  occurs  only  in  patches  within  the 
depressions  of  the  older  rocKS. 

Since  Cambrian  time  no  important  orographic  movements 
nor  outbursts  of  volcanic  material  have  occurred  in  the  Lake 
Superior  region,  consecjuently  the  rocks  have  received  little  sub- 
se(|ucnt  alteration.  To  these  facts  is  due  the  possibility  of  out- 
lining the  prc-Cambrian  history  of  this  area  with  greater  fullness 
than  has  been  done  in  areas  in  which  later  disturbances  have 
obscured  the  early  history. 

C.  R.  Van  Hise. 


I 


